How much money roughly will I need backpacking around Mexico for 3 weeks?

Please if anyone could give me a rough estimation in British Pounds of how much money I would need backpacking around Mexico (accommodation and spending money)

I am starting off in Mexico City and ending in Cancun, although I’d like to avoid the extreme touristy places. Obviously I know this will depend on whether I stay in posh hotels or hostels but just a rough guess to how much mixing the two.

I am going Jan/Feb.

Thank you very much!!